This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-048495, filed Feb. 23, 2001; and No. 2001-093869, filed Mar. 28, 2001, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a character projection type charged particle beam exposure system using an aperture mask. More particularly, the present invention relates to a charged particle beam exposure method, an exposure data processing method, an aperture mask, a method of manufacturing such an aperture mask and a recording medium storing an exposure program.
2. Description of the Related Art
Photolithography has been utilized broadly for manufacturing semiconductor devices because of simplicity of manufacturing process, low cost and other advantages. Technological innovations are constantly on the way. Micro-devices having a size less than 0.2 xcexcm may become available recently by using short wavelength laser beams (KrF excimer lasers). Efforts for developing ArF excimer lasers and Levenson type phase shift masks are being paid for the purpose of further fine pattern technology. They are expected to operate as mass production lithography tools corresponding to the 0.13 xcexcm rule. However, there are a number of problems to be dissolved and a long time may be needed before dissolving the problems. It is a matter of serious concern if the expected development of new mass production tools can keep pace with the desired fine patterning of devices.
On the other hand, electron beam lithography is the most expected candidate for replacing photolithography and it has been proved that it can deal with a dimension of 0.01 xcexcm by using a narrowed beam. While it may not be accompanied by any problem from the viewpoint of fine patterning, there may arise a problem of throughput when it is used for mass production tools for manufacturing semiconductor devices. More specifically, it is a time consuming operation to draw fine patterns one by one by means of electron beam lithography mainly because of a long exposure time. Apparatus employing a partial collective exposure method (character projection technique: CP technique) of collectively exposing repetitively appearing parts of an LSI pattern to electron beams have been developed in an attempt for dissolving the problem of consumption of time.
However, the use of such an apparatus is still not sufficient for catching up to the throughput of a manufacturing process using photolithography. This is because the number of stencil masks (character apertures) that are used for shaping a beam to make it conform to the shape of a repetitive pattern (a hundred at most) is by far short of the number of stencil masks necessary for exposing logic devices in order to realize a commercially feasible throughput (several hundreds to several thousands).
However, when manufacturing logic devices designed on the basis of standard cells (SCs) such as ASICs by using an electron beam (EB) exposure system, the number of EB shots can be efficiently reduced and consequently the throughput can be raised by using a character projection (CP) technique and extracting the character shape to be used for the exposure operation from the standard cell patterns that are used in the design stage.
Referring to FIG. 16 of the accompanying drawing, the electron beam generated by an electron gun 901 is made to show a rectangular cross section by a first shaping aperture mask 902 and selectively applied to a character aperture which is formed in a CP aperture mask 904 through a character selection deflector 903 and which has the shape of a character designed to operate as unit of exposure. As a result, the shaped electron beam is applied to a desired position of sample 907, which may typically be a resist film coated on a semiconductor substrate, by way of a reduction lens 905 that reduces the dimensions of the cross section of the shaped electron beam. In FIG. 16, reference numeral 906 denotes an objective deflector.
In the case where the CP aperture mask 904 does not include a desired aperture pattern, rectangular apertures for variable shaping may be employed. The pattern to be exposed is divided into a plurality of rectangles. In correspondence to the divided rectangles, the rectangular beam shaped by the first shaping aperture mask 902 is displaced by a desired distance and applied to the variable shaping aperture of the CP aperture mask, thereby producing respective rectangular beams each having a desired shape.
Thus, the number of patterns to be used for the exposure process that uses a variably shaped beam can be reduced for exposing a semiconductor device pattern designed on the basis of standard cells by providing the CP aperture mask with as many character apertures as possible then the character apertures show respective character shapes extracted from standard cells.
However, this method requires a shot for each standard cell. In other words, the number of EB shots cannot be less than the number of standard cells placed in the semiconductor pattern if the exposure operation is carried out ideally with the character projection technique.
Generally, a CP aperture mask is designed in a manner as illustrated in FIG. 17. Referring to FIG. 17, character-shaped apertures, or character apertures 1003 are arranged in each aperture block 1002 where any of the character apertures may be selected simply by electromagnetically deflecting the beam in a portion of the CP aperture mask 1001. The character apertures are two-dimensionally arranged in an array for every each largest beam size to be applied the aperture mask. In other words, a region corresponding to the largest beam size is allocated to any character aperture in the aperture block.
Therefore, with the known arrangement of CP aperture mask, the areas of the character apertures of the CP aperture mask (covering ratio) vary from place to place to make it difficult not only to effectively utilize the total area of the CP aperture mask but also to realize a high precision processing operation.
On the other hand, as an ingenious application of the partial collective exposure method, the applicant of this patent application has proposed a method of transferring only a part of apertures by applying a beam to it having a device pattern shape provided on a character aperture (Japanese Patent Application No. 2000-88967). With the proposed method, a rectangular beam shaped by first and second apertures (beam shaping apertures) is applied to a third aperture (character aperture) to transfer part of the profile of the aperture and exposing it to an electron beam.
A desired number of hole patterns can be collectively transferred by applying this exposure method to a contact hole of a semiconductor device. Therefore, the number of exposures can be remarkably reduced if compared with a variable beam shaping method of exposing holes one by one. However, while exposure data are required for selectively irradiating character apertures with an electron beam by means of this exposure method, no method of preparing exposure data has been developed to date.
According to the first aspect of the present invention, there is provided a character projection type charged particle beam exposure method for shaping a charged particle beam by using an aperture mask provided with character apertures corresponding to character shapes extracted from a semiconductor device pattern, which comprises:
arranging character apertures in the aperture mask, each of the character apertures having a shape corresponding to character shapes extracted from standard cells used for designing a semiconductor device; and
varying the shape of the charged particle beam according to the outer shape of each of the character apertures to apply the shaped charged particle beam to the character apertures.
According to the second aspect of the present invention, there is provided a character projection type charged particle beam exposure method for shaping a charged particle beam by using an aperture mask provided with character apertures corresponding to character shapes extracted from a semiconductor device pattern, which comprises:
arranging character apertures in the aperture mask, each of the character apertures having a shape corresponding to character shapes extracted from a pattern of a combination of neighboring standard cells in a designed semiconductor device pattern used for designing a semiconductor device; and
shaping the charged particle beam according to the outer shape of each of the character apertures to apply the shaped charged particle beam thereto.
According the third aspect of the present invention, there is provided a charged particle beam exposure method for transferring a plurality of aperture patterns simultaneously onto a sample by selectively applying a charged particle beam to character apertures each having a predetermined shape, which comprises:
outwardly moving at least a pair of opposite sides of a design pattern by a specified distance;
removing the overlap between patterns produced by the moving step and merging the patterns;
dividing the patterns obtained by the merging step into a plurality of rectangles;
shaping to charged particle beam depending upon the rectangular data obtained by the dividing step; and
applying the shaped beam to a plurality of aperture patterns.
According to the fourth aspect of the present invention, there is provided an aperture mask used for a character projection type charged particle beam exposure, which comprises character apertures each having an opening shape corresponding to a shape of a character extracted from standard cells used for designing a semiconductor device, each of the character apertures being arranged according to respective shapes.
According to the fifth aspect of the present invention, there is provided a method of designing an aperture mask, which comprises:
extracting a shape of a character from the patterns of standard cells used for designing a semiconductor device; and
arranging character apertures in the aperture mask according to their shapes, each of the character apertures having a shape corresponding to the shape of the extracted character.
According to the sixth aspect of the present invention, there is provided a method of producing exposure data used for a charged particle beam exposure for simultaneously transferring a plurality of aperture patterns on a sample by selectively applying a charged particle beam to character apertures including periodically arranged aperture patterns and for defining the shape of the charged particle beam to be applied to the character apertures, which comprises:
outwardly moving at least a pair of opposite sides of a design pattern by a specified distance;
removing the overlap between patterns produced by the moving step and merging the patterns;
dividing the patterns obtained by the merging step into a plurality of rectangles; and
providing the rectangles obtained by the dividing step as exposure data.
According to the seventh aspect of the present invention, there is provided a computer-readable recording medium which stores a program for controlling a charged particle beam exposure system by means of a computer and for selectively applying a charged particle beam to character apertures including periodically arranged aperture patterns with predetermined shapes, thereby simultaneously transferring the aperture patterns to a sample, the program controlling the computer to execute the followings:
outwardly moving at least a pair of opposite sides of a design pattern by a specified distance;
removing the overlap between patterns produced by the moving step and merging the patterns;
dividing the patterns obtained by the merging step into a plurality of rectangles;
shaping the charged particle beam depending upon the rectangular data obtained by the dividing step; and
applying the shaped beam to a plurality of aperture patterns.